Add native error derive macro

[RAprogramm]

Summary

• add a masterror-derive proc-macro crate that reimplements the Error derive using the shared parser from masterror-template
• expose the new macro from masterror::Error and re-export the template helpers from the internal crate
• update documentation and changelog to describe the native derive

Testing

• cargo clippy -- -D warnings
• cargo +nightly fmt --
• cargo build --all-targets
• cargo test --all
• cargo doc --no-deps
• cargo test --test error_derive_from_trybuild

---

https://chatgpt.com/codex/tasks/task_e_68cca81c89d0832b95fbcceefc305db1

[chatgpt-codex-connector]

Codex Review: Here are some suggestions.

masterror/masterror-derive/src/error_trait.rs

Lines 52 to 58 in d15ee64

	match display {
	DisplaySpec::Transparent {
	..
	} => {
	if let Some(field) = fields.iter().next() {
	let member = &field.member;
	quote! { std::error::Error::source(&self.#member) }

[P1] Preserve wrapped error in transparent source()

When deriving #[error(transparent)], the generated source() calls std::error::Error::source(&self.#member) instead of returning the wrapped field itself. This skips the immediate cause in the error chain: a transparent wrapper over io::Error will now return None because it queries io::Error::source() rather than returning Some(&io_error). Downstream consumers walking the chain will miss the wrapped error entirely. The transparent impls should return the field (or its Option contents) as the source, mirroring thiserror, instead of delegating to the inner error’s own source().

---

Reply with @codex fix comments to fix any unresolved comments.

About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you open a pull request for review, mark a draft as ready, or comment "@codex review". If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex fix this CI failure" or "@codex address that feedback".